vm overcommit handling

[Werner Almesberger]

David Kuehling wrote:
> So are you ok with such a change?

Sounds like the right thing to do to me. Tying VM size to RAM size can
serve as an early warning on larger boxes, but it doesn't seem to make
much sense on memory-tight devices like the Ben. Also, without swap,
there's no risk of thrashing.

- Werner